This invention relates to a digitally tuned antenna suitable for airborne use.
New radios have been developed which are capable of operating in both the VHF and UHF bands, and capable of fast switching between frequencies. It is an object of the present invention to provide an antenna system compatible with such radios and suitable for airborne use.
An airborne antenna must be small, so that among other things, it does not create excessive drag. A small antenna for these frequencies is quite inefficient, unless it is tuned to the particular frequency being used. Accordingly, an approach to providing a small airborne antenna which is useful over a relatively wide band is to make the antenna tunable over the band.
An existing antenna which deals with some aspects of this problem is the 437-1 VHF/FM Blade Antenna system of Rockwell International Corporation. At a first terminal of the radiating element of this system, is the radio frequency input, an inductance and a saturable reactor used for fine tuning. Also at this terminal is a phase discriminator for detecting phase as a measure of the extent to which the antenna is in or out of tune. Connected to the other terminal of the radiating element is a servo-driven variable capacitor for tuning the antenna. The output of the phase discriminator is used as an error signal to drive the capacitance to a value which tunes the antenna.